Flower buds are formed in a period when higher plants convert their growth from vegetative growth to reproductive growth. In this period, many genes express as the functions and forms of the plants change. It is therefore of significant importance to obtain a gene expressed specifically at initial stages of flower-bud formation and its promoter to provide a means for clarifying the mechanism of reproductive growth and for genetically engineering plants in their reproductive growth period.
However, the mechanism of flower-bud formation has not been fully clarified, and, in particular, no gene that is involved in flower-bud formation or promoter that induces its expression are known.
On the other hand, cytochrome P450 in higher plants is known as a gene which is involved in 1. secondary metabolism of flavonoids and alkaloids, and 2. metabolism of chemicals such as herbicides. Examples of cytochrome P450 involved in the secondary metabolism include cDNA for cinnamate 4-hydroxylase, flavonoid-3'-5'-hydroxylase, jasmonate synthase, and salicylate hydroxylase which have been cloned and are known to be concerned with biophylaxis, and biosynthesis and metabolism of phytohormones and signal substances. It is known that cytochrome P450 genes consist of many groups of genes called superfamily, and it is also known that the homology of amino acid sequences in a family equals to, or more than 40% (Nebert et al. DNA Cell Biol. 10, 1-14, 1991). No presence of a cytochrome P450 that specifically expresses at initial stages of flower-bud growth has been known heretofore.